Tire sidewalls are often coated with protective paints or coatings, particularly tire sidewalls having a color which contrasts with the typical black colored remainder of the tire. The general purpose of such a protective coat or painting is to inhibit or prevent migration of chemicals to the tire rubber composition from the surface of an adjacent black colored tire which would otherwise tend to stain and thus, discolor the rubber. The staining usually becomes evident after exposure of the contacted rubber surface to ultra-violet light such as sunlight. Such contact staining phenomenon is well known.
A water soluble polyvinylalcohol (PVA) based coating is often used for such protective coating for tire sidewalls, particularly white tire sidewalls.
White sidewall pneumatic rubber tires are sometimes mounted, aligned and balanced on metal rims on an automated basis which involves detection of a highly ultraviolet reflective (fluorescent) label placed on the coated tire white sidewall. Unfortunately, a PVA based coating on the white sidewall, which also overcoats the label, can also be highly reflective and thus, interfere with the label detection and associated mounting, alignment and balancing of the tire on the rim.
The label detector apparently becomes confused and does not effectively discern an adequate differentiation between the label and the PVA coating.
Thus, in one aspect, it is desired to provide a tire sidewall, particularly a pneumatic rubber tire white sidewall, having a PVA-based coating thereon which does not substantially interfere with detection of an ultraviolet reflective label on said tire surface while maintaining a stain resistant quality.
Rubber tires are typically black in color due to the carbon black reinforcement contained therein. If a contrasting or other color is desired for a part of the tire, then a coloring pigment is used rather than the carbon black. Conventionally, various of the compounding ingredients used in the formulation of rubber for the manufacture of rubber products such as tires are of the staining type, namely, amine based antidegradants and aromatic rubber processing oils. The materials tend to migrate to the surface of the rubber and may stain or discolor a rubber surface of another rubber article which may come in contact with it for a period of time, the discoloration typically becoming evident after the contacted rubber is then exposed to ultra-violet light.
Thus, often, a polyvinylalcohol (PVA) based coating is used to protect such contrastingly colored rubber surfaces from other rubber surfaces of the staining type because the polyvinylalcohol itself tends to be a barrier for the migration of such staining material. Moreover, the PVA can normally be easily removed from the coated rubber surface, when and if desired, by simple water washing, usually with a soap solution, since the PVA itself normally has a relatively high degree of water solubility. Thus, the PVA coat has a primary use for storage and shipping of the tires. It may easily be removed by the user by water washing. The general use of PVA for such purpose is well known.
PVA is normally used for such purpose in conjunction with (mixed with) a plasticizer therefor, including at least one of polyglycerol, diglycerol and glycerin, so that the resulting PVA-based coating has a degree of flexibility. Such PVA mixture is referred to herein as PVA coating and can have a relatively high degree of reflectivity.
Accordingly, it is desired to provide a coating composition and a resultant coated rubber product, particularly a coated tire sidewall rubber surface, which will retard, inhibit and/or prevent the migration of amine based antidegradants and aromatic processing oils onto the rubber sidewall surface, such as a white sidewall, from an adjacent and contacting black rubber surface, yet still enable a detection of an ultraviolet reflective label on the surface of the tire and maintaining a stain resistant quality of the PVA-based coating.